1. Field of the Invention
The present invention relates to a process apparatus having coated aluminum-based members, a method for coating aluminum members, and a method of forming a bonding portion.
2. Description of the Related Art
In a CVD apparatus used for forming an insulating film or a thin silicon film on a semiconductor wafer surface, a support table is provided within an airtightly constituted process chamber and a semiconductor wafer to be processed is placed on the support table. The process chamber is evacuated to, e.g. about 10.sup.-6 Torr, a predetermined process gas is introduced into the process chamber, and a predetermined thin film is formed on the semiconductor wafer.
A heating apparatus such as a heater may be provided, in some cases, below the support table. The heating apparatus is supplied with a power from, e.g. an AC power supply to heat the wafer on the support table up to a predetermined temperature.
The surfaces of the support table provided within the process chamber of the CVD apparatus, the inner walls of the process chamber, etc. are generally formed of an aluminum-based material subjected to alumite treatment (anode oxidation treatment).
If the thin film is formed by the CVD apparatus on the wafer or the object to be processed, as mentioned above, a reaction product adheres to the surfaces of the support table, the inner walls of the process chamber, etc. at each time of formation.
Since the process chamber requires a very clean internal atmosphere, a cleaning gas is introduced into the process chamber to remove the reaction product each time a predetermined number of times of the process have been completed. As this kind of cleaning gas, attention is paid to ClF.sub.3 and NF.sub.3 gases which are excellent in removing reaction products.
However, since the ClF.sub.3 and NF.sub.3 gases have very high reactivity, the inner walls of the process chamber and the support table themselves are etched. The lifetime of these members are shortened and, in some cases, the process is deteriorated.
On the other hand, there is, for example, an etching process apparatus as another process apparatus for processing a semiconductor wafer in a semiconductor manufacturing step. In this etching apparatus, a support table functioning as a lower electrode is situated within a process chamber serving as an airtight chamber with a reducible pressure. A semiconductor wafer is brought into the process chamber from an opening formed in a side wall of the process chamber via an opening/closing means, e.g. a gate valve, and is placed on the support table. A RF supply is connected to the support table via a blocking capacitor. An upper electrode is provided so as to face the support table functioning as lower electrode. A gas introducing pipe for introducing a process gas into the process chamber is connected to the upper electrode. That surface of the upper electrode, which faces the support table, is provided with small holes. The process gas is guided towards the semiconductor wafer via the gas supply pipe and small holes.
The upper electrode is electrically grounded. When the RF power supply is turned on, a RF power is applied to the support table. Thereby, an electric field is generated, and the process gas is made into a plasma by the electric field.
The upper electrode comprises a plurality of electrically conductive members, for example, aluminum-based top wall, side walls and bottom wall. The surfaces of these members are subjected to alumite treatment and insulating layers are formed thereon. In order to prevent abnormal electric discharge, these members are electrically conductively connected to have an equal potential. In order to connect these members, the bottom wall is provided with a recess for bonding with the side walls.
However, the surface of the bottom wall is subjected to alumite treatment, as described above, and the insulating layer is formed thereon. In order to form the recess, the base material or aluminum is exposed directly by a machining process. Of course, the alumite layers on the contact faces of the side walls, which come into contact with the recess, are removed, and the base material or aluminum is exposed. Thus, electric conductivity between the side walls and the bottom wall is attained, and these members are set at a predetermined potential. These side walls and bottom wall are fixed and coupled by means of, for example, bolts.
In this etching apparatus, however, the plasma is generated within the process chamber. Thus, the exposed aluminum portion of the recess in the bottom wall, which is other than the contact portions with the side walls, is etched by an active species, e.g. ions, in the plasma. Thus, etched matter is dispersed as particles within the process chamber. If the particles adhere to the object to be processed, the yield of processed objects decreases.
Moreover, in many kinds of semiconductor process apparatuses other than the etching apparatus, many kinds of corrosive gases, e.g. chlorine-based gases, are generally used. Such gases corrode the exposed aluminum portion and corroded portion is dispersed as particles within the process chamber.
The corrosion occurs not only at the exposed aluminum portion but also at the contact portion between the bottom wall and side walls, and electric conductivity at the corroded portions becomes unstable. If the corrosion further processes, the electric conductivity is lost. As a result, a potential difference occurs among the members, and an abnormal electric discharge occurs in an apparatus which generates a plasma.
If such an abnormal electric discharge occurs, particles will occur and moreover impedance matching with the high-frequency power supply will be lost. If the impedance matching is lost, the supply of RF power becomes unstable. If objects to be processed are processed in this state, the yield of processed objects will decrease.